<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .box {
      width: 200px;
      height: 200px;
      border: 1px solid black;
      background: yellowgreen;
      /* 标准盒模型 */
      /* box-sizing: content-box;    */

      box-sizing: border-box;



      padding: 10px;
      
    }
  </style>
</head>

<body>
  <!-- 
    
    //标准盒模型： width ===>content的width
  //怪异盒模型： width ===>content+padding+border的width

-->
  <div class="box">

  </div>
</body>

</html>